Devices of this type have already been disclosed, for example in U.S. Pat. No. 6,220,909 B1. That document describes an avalanche airbag inflation device intended to operate notably using a cartridge of nitrogen compressed to 200 bar. The cartridge is assembled with a control mechanism that allows the gas to be released in response to a user action. The gas, once released following the piercing of the cartridge, is conveyed to two inflation mechanisms, by pipes, each inflation mechanism being associated with an inflatable bag.
The gas is injected into a cylindrical air intake chamber provided in each of the inflation mechanisms by an injection nozzle arranged substantially in line with the central axis of the air intake chamber. This chamber comprises a plurality of openings in its lateral wall so that atmospheric air can be sucked in in response to the injection of the high-pressure gas. The air sucked in is accelerated by a Venturi effect to inflate the corresponding inflatable bag quickly with a sufficient volume, by applying a multiplication factor (volume of air/volume of compressed gas) to that of the volume of compressed gas available, thanks to the addition of the air.
Each of the inflation mechanisms further comprises a nonreturn check valve to prevent the corresponding inflatable bag from becoming deflated via the inlet when it is fully inflated.
As an alternative to nitrogen, it is also known practice to use compressed air, which is a mixture of oxygen and nitrogen and some traces of other gases, as the compressed gas at high pressure.
In general, the multiplication factor applied in the known devices is not very high, of the order of 2 to 3 (which means that the volume of atmospheric air injected into the airbag is of the order of 2 to 3 times the volume that the gas represents in the airbag once it has expanded) and entails the use of a significant volume of compressed gas in order to be able to inflate the airbag.
The space occupied by the compressed-gas cartridge thus contributes significantly to the overall space occupied by the inflation device, and this is why the abovementioned US patent proposes a design of the device that comes in modular form, which means to say that allows the various component parts of the device to be located at different parts of a pack for example.
However, in that case, getting the device into or out of a backpack, for example, is a complicated matter because each of its component parts has its own means of attachment that have to be done up or undone.
It will also be noted that, aside from the requirement that has to be observed regarding the airbag inflation volume, it is absolutely essential that the airbag be inflated quickly. As a general rule, an avalanche airbag needs to be inflated in around 2 to 4 seconds, preferably in less than 5 seconds.
EP 258619 A2, discloses a device as herein described, comprising an intermediate distribution chamber for the compressed gas, which chamber may be arranged between the inlet and the air intake chamber in order to connect the one to the other, and a plurality of ejection holes arranged so as to open into a lateral wall of the air intake chamber in order to connect the latter to the intermediate distribution chamber.
By virtue of these features, the device can be used with carbon dioxide cartridges which were not useable with devices according to the state of the art. Further, said device is adapted for use with different gases, such as nitrogen.
Carbon dioxide is a gas which is highly compressible and can be stored in a liquid form, which means that a large potential volume of it can be stored in a cartridge of the kind frequently used in various applications. This is one of the reasons, aside from its low cost, why this gas is generally used for inflating lifejackets in vehicles of the boat or aeroplane type, for example.
However, the expansion of this gas consumes a great deal of energy, which causes it to cool rapidly as it expands and carries with it the risk of it freezing. The device as disclosed in foresaid application however makes it possible to avoid these difficulties which are specific to carbon dioxide and to harness all the advantages of its use with reference to the other gases.
As illustrated in a preferred embodiment of said former application, said device could have two inlets which allows the use of two cartridges with a small volume instead of one cartridge with a huge volume. The risk of freezing of the carbon dioxide was reduced.
The use of said device with carbon dioxide still might have some limitations, in particular depending on surrounding temperature. Indeed, with ambient temperatures of below 0° C., the viscosity of carbon dioxide increases. Such a high viscosity results in a slow release to the air intake chamber, resulting in a significant lengthening of inflation the airbag.
With ambient temperatures below −10° C., the expansion of carbon dioxide can cause freezing of the carbon dioxide and can lead to a malfunction of the device.
At this end, at least a partial risk of freezing remains, even in extreme conditions, particularly in ambient temperatures below −10° C. For temperatures below 0°, an effect of decelerating of the distribution of gas, and thus, decelerating of inflation of the inflating bag occurs.
In consequence, said known device reliably works in common ambient temperatures. However, it may not always reach a sufficiently reliable level in extreme conditions which maybe necessary for official certification.